I accidentally found Wikipedia in July 2004 while doing a web search. I've been making occasional edits to it since September 2004, and I also use it as a reference tool.

its & it'sThis user understands the difference between its and it's. So should you.
their
there
they're
This user thinks that there are too many people who don’t know that they're worse than their own children at spelling!
A, B, and CThis user prefers the serial comma.
You and MeThis user thinks that if you believe it is incorrect to use "you and me" as the object of a sentence, a little talk needs to be had by you and me...